12 PERCY SLADEN TRUST EXPEDITION 
thick, gastral cortical skeleton, continued for some distance into the main exhalant canals 
and consisting of small triradiates and quadriradiates with long, slender apical rays. 
There are no subgastral nor subdermal sagittal or pseudosagittal radiates, but small 
sagittal radiates* occur as usual in the thin and rather narrow oscular collar. 
The spicules are all equiangular and approximately equiradiate, and there are two 
chief forms :— 
(1) Very large triradiates (Plate 4, fig. 3, a), with stout rays tapering gradually 
to fairly sharp points and measuring about 1:0 by 01 mm. 
(2) Small triradiates (Plate 4, fig. 3, b), with rather slender rays measuring about 
0°17 by 0:0125 mm. 
Both forms are abundant and they occur intermingled at the surface and in the 
chamber layer, but the small ones are much more numerous than the large ones, while 
intermediate sizes (Plate 4, fig. 3, c) occur in much smaller numbers. 
The quadriradiates of the gastral cortex differ only from the small triradiates in the 
development of the long, slender apical ray, while the sagittal triradiates of the oscular 
collar are but shght modifications of the ordinary small form, with the two oral arms bent 
back till they he approximately at right angles to the basal arm. 
The specimens are not well preserved from the histological point of view, but the 
nuclei of the collared cells are basal. 
This species differs from Leucetta chagosensis in its well-defined external form, in the 
presence of the large triradiates in the chamber layer, as well as in the dermal membrane, 
in the spicular measurements and in the presence of the gastral quadriradiates. It comes 
closer to Leucetta microraphis, as represented by my Australian specimens, but again 
differs in the well-defined external form, consisting of only a single person of very 
definite shape. 
It may quite possibly be identical with one of the numerous forms included by 
Haeckel [1872] under his Leucetta primigena, but I do not think it possible to dis- 
entangle all these forms from one another. 
Register Nos., Localities, dc. xc. 5, A and B, Cargados Carajos, 1.9.05, B. 29, 
45 fathoms. 
Genus PERICHARAX Poléjaeff (emend.). 
Colony individualised, with large central cavity opening by a wide osculum and 
surrounded by a very thick wall. Canal system leuconoid, with subspherical, scattered 
chambers, and with subdermal cavities whose walls are supported by a special skeleton 
derived partly from inturned rays of tangential dermal triradiates. Skeleton of chamber 
layer confused, composed of equiangular triradiates of two very different sizes. 
Poléjaeff [1883] proposed the genus Pericharax for the reception of two specimens 
obtained by the “Challenger” at Tristan da Cunha, which he regarded as representing 
_ two varieties of one and the same species, Pericharaz carteri. The one variety he named 
* These have been dissolved out, but their spicule sheaths are still clearly recognizable and give the form 
quite distinctly. 
